Conventional suspensioning systems, especially those of large highway trucks, have generally been accomplished with leaf springs which are difficult to design so that a soft vehicle spring rate for ride characteristics can be provided with sufficient stiffness against roll to provide stability against lateral forces. Additional stabilizing bars and equipment have been used. Ordinarily, such springing of trucks provides a very hard ride. A compromise has been required, resulting in a stiff spring rate in up and down direction in order not to allow too soft a spring rate against roll of the vehicle under lateral force loads.
Air springs have been utilized in trucks and busses to support vehicle weight and load weight. Stabilization of the vehicle against roll has generally been provided in addition to such air springs and separate therefrom.
Vehicle roll stiffness has been achieved separate and apart from the springing by the use of hydraulic shock absorber units connected across a vehicle. U.S. Pat. No. 3,328,019 and British Pat. No. 1,335,758 (1973) are typical of such.
There has been a use of air springs on auxiliary load supporting axles of highway trucks. Generally, such air springs support part of the truck load to the axle. In some instances, auxiliary air springs have been used to raise the axle and its tires from contact with the road for avoiding tire wear when the truck is running empty. U.S. Pat. Nos. 3,201,141, 3,290,056 and 3,390,895 are typical of such auxiliary axle constructions.